1. Field of the Invention
The present invention relates to a method of biodegradation of a polluting substance, which method employs an auxotrophic microorganism and is useful for environment protection.
2. Related Background Art
In recent years, various harmful and non-decomposable chemical substances have come to be detected in soil, river, sea, air and other environments, and the environmental pollution has become highlighted. The adverse effects given by such substances are become a matter of great concern. Therefore, prevention of pollution and remediation of the environment from pollution are strongly demanded. An example of environment remediation technique is a strengthening of functions of microorganisms in the ecosystem to decompose the polluting substances into non-polluting substances. This technique intends to stimulate the natural degradation processes, to promote the decomposition of the polluting substance. This technique is further advanced to introduce intentionally from the outside a microorganism having an ability of decompose a polluting substance to promote remediation of a polluted area to a non-polluted state. Biodegradative clean-up technology is demanded in various fields such as treatment of polluted soil in gas production plant sites, oil refinery plant sites, sites of a demolished petroleum refinery, sites of a demolished fuel stockyard, sites of a demolished pulp plant; cleaning of lakes and marshes, rivers, sea water, underground water, and the like; treatment of drinking water and industrial water; treatment of industrial waste water and living waste water; and so forth. Pollution of soil may cause spread of the polluted area by diffusion of the polluting substance with underground water, and pollution of river or the like may cause spread of the polluting substance with flow of water over the basin or the shore. Therefore, an effective method for removal of polluting substance from soil and water is strongly demanded.
Although various physical and chemical methods are known for removal of polluting substances, few of the methods are satisfactory from a standpoint of cost, ease of operation, and decomposition efficiency. For soil treatment, for example, a vacuum extraction method is available which sucks out the polluting substance from the soil. This method; however, is unsatisfactory in view of the cost, ease of the operation, and the efficiency of elimination of the polluting substance.
Therefore, a biodegradation method is attracting attention to offset the disadvantages of the physical and chemical methods.
However, if a microorganism for biodegradation is applied in a high concentration to soil or river, the ecosystem in the applied area will be changed. Such change of ecosystem is not favorable for environmental protection. The ecosystem in the treated area should desirably be restored to the original state when the polluting substance has been removed or decomposed. Furthermore, if the microorganism diffuses out unnecessarily from the polluted area during the biodegradation, the diffused microorganism itself may possibly cause secondary pollution or other hazard. Ideally, the microorganism introduced from the outside should work only in the polluted area, and become extinct spontaneously after the environment is remediated. In particular, in use of a microorganism in open systems such as soil, lake, marsh, river and sea, the fate of the microorganism is a great problem.